{smcl}
{* 22aug2004}{...}
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{center:{hi:Why {cmd:twoway}'s plottypes are convenient}}
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{p 4 4 4}{it}
Draw a few simple {cmd:twoway} graphs by clicking the next 4 commands.
{sf}

. {stata  sysuse uslifeexp , replace}
. {stata  keep if year <= 1940}

. {stata  twoway scatter le year}
. {stata  twoway line le year}

{p 4 4 4}{it}
Now, draw a simple {cmd:twoway} with two plots.
{sf}

. {stata  twoway scatter le year || lfit le year}

{p 4 4 4}{it}
There are some options that make sense only to {cmd:lfit} and not
to {cmd:scatter}.  For example, we can ask {cmd:lfit} to produce
residuals rather than predictions of the dependent variable by
using the option {cmd:predopts(resid)}.  A {cmd:predopts()} option would
not make sense on a {cmd:scatter} plottype.  So, having the plottype
appear early in the command lets us parse plottypes differently and
allows each plottype to have unique options.  Let's, draw the fit with
residuals by clicking below.
{sf}

. {stata do twoway0a:twoway scatter le year ||}
	 {stata do twoway0a:lfit le year    ||} 
	 {stata do twoway0a:lfit le year , predopts(resid)}

{p 4 4 4}{it}
{cmd:lfit} assumes that you are drawing a fitted line and so creates a 
{cmd:line} plottype.  That is not a very good way of plotting residuals,
but we can change to most other twoway plottypes by using the 
{cmd:recast()} option to "recast" the plot to another plottype.  Let's
make our residuals {cmd:dropline}s. (click below)
{sf}

. {stata do twoway0b:twoway scatter le year ||}
	 {stata do twoway0b:lfit le year ,  ||} 
	 {stata do twoway0b:lfit le year , predopts(resid) recast(dropline)}

{p 4 4 4}{it}
The {cmd:recast()} option is available on almost all twoway plottypes and
on most statistical graphics commands.

{p 4 4 4}{it}
The syntax of plottypes in the twoway command makes plottypes almost
most complete commands in themselves.  We can even apply an {cmd:if} or 
an {cmd:in} condition to a single plottype.  We do that below on the 2nd
linear fit ({cmd:lfit}), restricting its data to years prior to 1920. (click below)
{sf}

. {stata do twoway0c:twoway scatter le year ||}
	 {stata do twoway0c:lfit le year	 ||}
	 {stata do twoway0c:lfit le year if year < 1920}


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{center:{view cmds.smcl:<<}   {view tindex.smcl:index}   {view anatomy101.smcl:>>}}